1. Field of the Invention
The present invention generally relates to a method and an assembly for braking a selectively movable assembly and more particularly, to a vehicular brake assembly which provides a controllably varying amount of self energization and to a method for braking a selectively movable assembly which provides this controllably varying amount of self energization by the use of a pair of selectively movable wedge members which cooperatively allow a vehicle to be smoothly and efficiently braked with the use of a pair of relatively small electrical motors.
2. Background Art
An electromechanical braking assembly typically 20 provides braking of a selectively movable assembly (such as a vehicle) by the use of a motor which becomes selectively energized upon a sensed depression of a brake member. At the outset, it should be appreciated that the term “selectively movable assembly” refers to any assembly, including but not limited to a vehicle, which has at least one wheel which may be selectively rotated and which must be selectively braked. Hence, it should be realized that the present invention is applicable to a wide variety of such selectively movable assemblies and is not limited only to a vehicle. Further, while the terms “vehicle” and “selectively movable assembly” may be interchangeably used in this description, the present invention is not limited to a vehicle or any other particular type of selectively movable assembly.
Particularly, such an electromechanical braking assembly typically includes a rotor which moves with the wheel of the vehicle or other selectively movable assembly in which the electromechanical braking assembly is operatively disposed and a pad which is made to engage the rotor, by the selectively activated motor, effective to brake the moving wheel and thereby brake the selectively movable assembly. Importantly, such an electromechanical braking assembly does provide some advantages over traditional hydraulic brake systems. One non-limiting example of such an electromechanical brake assembly is described within European Patent Number EP 0953785A3 which is fully and completely incorporated herein by reference, word for word and paragraph for paragraph.
By way of example and without limitation, such an electromechanical braking system provides the desired braking in a substantially shorter amount of time than that which is provided by a conventional hydraulic braking system and allows each of the individual wheels of a vehicle or other selectively movable assembly to be selectively controlled, thereby enhancing the effectiveness of many operating strategies such as an anti-skid or anti-lock braking strategy or a strategy which is commonly referred to as an “integrated vehicular dynamic” strategy.
However, while such an electromechanical braking system provides these and other advantages, it requires a relatively large motor which increases the overall cost of producing the vehicle (or other selectively movable assembly) while concomitantly and undesirably requiring a relatively large packaging space which may require a modification in the packaging design of many assemblies, such as vehicle assemblies, which have respectfully and relatively “tight” space constraints or requirements. Further, the relatively large motor requires a relatively large amount of electrical power in order to operate, thereby requiring a relatively large battery or power source, in excess of that which is conventionally placed within a vehicle, thereby further and undesirably increasing the overall production cost of the vehicle or other selectively movable assembly.
Further, current electromechanical brake systems utilize only a single motor and this architecture may be undesirable since these systems may not provide a desired amount of braking in the event that the single provided motor is not activated. In contrast to the “single motor” electromechanical braking system, an electro-hydraulic braking system normally utilizes a manual second or “back up” braking assembly which brakes the vehicle or other selectively movable assembly in the event of that desired braking is not provided by the “primary” electro-hydraulic braking assembly. Although this approach does provide the desired redundancy, it undesirably increases the cost of producing the vehicle, undesirably increases the amount of required packaging space, and, as earlier delineated, does not provide all of the features and benefits associated with an electromechanical braking system.
One attempt to overcome these drawbacks requires the use of a self-energization member, having at least one or more substantially identical wedges which are deployed upon or provided by a single wedge member, and which is typically deployed within the electromechanical braking system. Particularly, the at least one wedge (as well as the other wedges) has a fixed angle of inclination that provides additional mechanical advantage and assists in “forcing” the brake pad against the rotor, thereby reducing the amount of braking actuation power which must be provided by the motor. Importantly, it is the shape or geometric configuration of the at least one wedge which assists the motor in braking the assembly, thereby conserving energy (e.g., the physical or mechanical properties of the at least one wedge provide this desired “brake enhancing” functionality without requiring additional activation energy or power from the motor). Hence, a member which “provides” such a wedge is referred to as a “self-energization” member. While this approach does reduce the overall power requirements and the size of the motor, it too has several drawbacks.
For example and without limitation, a conventional electromechanical self-energizing braking system provides a fixed amount of self-energization (an amount which is not selectively variable by a controlled amount and which is wholly determined by the fixed angle of inclination of the at least one wedge as the selectively movable assembly moves in a certain direction), even though the amount of friction between the rotor and the pad varies with temperature, humidity, and other environmental conditions. Therefore, this arrangement requires the operator of the selective moving assembly to vary the amount of pressure or force which is exerted on the braking member in order to achieve the same amount of braking as these environmental conditions change during the operation of the selectively movable assembly, thereby undesirably causing the operator to have an inconsistent braking “feel”. Further, this approach does not allow for the use of a relatively low powered motor since the motor must be capable of operating under conditions in which the amount of friction between the rotor and the pad is relatively high and when the amount of friction between the rotor and the pad is relatively low. The inability of the motor to operate under these extreme frictional conditions might cause the brake assembly to undesirably enter a tension mode (e.g., a mode in which the motor must overcome the friction force which is pulling the pad in the same direction as the rotor is moving in order to reduce braking force) from a desired compression mode (e.g., a mode in which the motor pushes the pad in the same direction as the rotor is moving in order to generate a brake force).
That is, during a compression mode of operation which occurs when the frictional force is relatively low, an “undersized motor” (e.g., a motor which does not provide enough actuation force to ensure desired operation in high and low friction conditions) may not be capable of generating the deceleration desired by the operator. During a tension mode of operation, which occurs when the frictional force is relatively high, an “undersized motor” may not be able to pull the pad with enough force to prevent it from being frictionally “locked” onto the rotor, thereby preventing the braking assembly from providing the desired braking required by the operator.
Further, while the current electromechanical braking configuration, in the desired compression mode, provides a high gain at one level of friction (e.g., during high friction), it will provide a much lower gain at lower friction levels. This means that a larger actuating motor must be utilized than would be necessary if the wedge angle or the angle of inclination could be “optimized” (i.e., dynamically configured to provide large amounts of brake enhancement at each friction level). Hence, due to the use of a fixed amount of self-energization (emanating from the use of a fixed angle of inclination), a relatively large motor must be employed to ensure that the braking assembly functions during “worst case” situations in which a large amount of activation power is required.
Moreover, yet additional drawbacks exist if a single and relatively small motor were utilized in a conventional electromechanical braking system which is designed to operate in both the compression mode and the tension mode. That is, the relatively small motor must overcome the inertia associated with existing compression braking in order to provide tension type braking, thereby resulting in a relatively slow response time which provides an uncomfortable “feel” to the operator of the selectively movable assembly. Moreover, the braking assembly, in overcoming such inertia, may even provide an undesirable amount of compression or tension type force. In fact, at one instant of time, during this transition, the motor neither provides compression nor tension and at this “zero point”, the braking assembly may not function in a desired manner.
The present invention overcomes these drawbacks in a new and novel fashion by allowing for a controllably varying amount of self-energization to occur as the amount of friction between the rotor and the pad varies.